Rain can spoil a wolf spider’s day, too

Wolf spiders change their mating strategy after it rains

If you hate the rain, you have something in common with wolf spiders.

Researchers at the University of Cincinnati found that wolf spiders can’t signal others or perceive danger from predators as easily on rain-soaked leaves compared to dry ones. Even communicating with would-be mates is harder after it rains.

The study was published in the Journal of Insect Behavior.

Professor, Biological Sciences Dr. George W. Uetz holds one of his male spider in his lab at Rieveschl Hall.  UC/ Joseph Fuqua II

UC College of Arts and Sciences Professor George Uetz and his students are learning how climate change might affect spiders and their predators. Photo/Joseph Fuqua II/UC

Biologists in UC’s College of Arts and Sciences studied Schizocosa ocreata, a wolf spider found across much of the United States. Males respond to chemical signals from females by using a combination of visual and vibratory signals for courtship.

Spiders don’t have ears, but sense sound in vibrations using specialized sense organs in their eight legs. The vibrations from sound carry much better in dry leaves.

Wolf spiders are especially attuned to the calls of predatory birds like blue jays that feast on spiders, particularly during nesting season when their offspring eat virtually nothing else, lead author and UC Professor George Uetz said.

“Birds preferentially feed spiders to their offspring because spiders have 50 times the amount of taurine than insects,” Uetz said. “And taurine is critical for the development of the hippocampus of nestlings’ brains. The hippocampus is associated with spatial memory, which is really important for birds.”

a pair of wolf spiders on a leaf.

UC biologists discovered that wolf spiders can't communicate with potential mates as easily after it rains. They must rely more on visual communication rather than chemical or vibratory cues. Photo/Joseph Fuqua II/UC

The spring nesting season coincides with the spiders’ mating season. Male wolf spiders are especially vulnerable to birds when they try to woo a mate with a flashy display, which involves drumming their exaggeratedly furry front legs on the leaves in front of them.

The UC study found that male spiders become motionless and “freeze” when a blue jay calls nearby. And they stay frozen longer on dry leaves than on wet ones, possibly because the dry leaves provide a better early warning than wet ones that dampen vibrations.

Uetz said the striped black and brown spiders have remarkable camouflage when they remain motionless.

“If they remain still, they just disappear,” he said.

Spiders are very important to local ecosystems, both as a predator of insects and as a major food source to larger animals like birds.

Rachel Gilbert, UC graduate

“Like lots of predators, blue jays are visually oriented,” Uetz said. “They’re very visually acute. For them, movement really is the key.”

With climate change increasing the frequency and duration of spring rains, wolf spiders will face increasing ecological challenges, Uetz said.

“Spring is coming a little earlier. What we’re seeing is there’s a shift in the life cycle of the spiders,” Uetz said. “If global warming shifts the annual life cycle of the spiders, that will push them out of synchrony with the nesting season of the birds, which is more closely tied to daylight cues.”

Wet leaves didn’t discourage male spiders from courting females. Male spiders increased visual signaling to compensate for the inability to use vibrations. But spiders that could use dry leaves to communicate to females had more mating success. 

A biology student holds a wolf spider on her finger in front of her face.

Despite their fearsome name, wolf spiders are harmless. Photo/Joseph Fuqua II/UC

UC graduate Rachel Gilbert, a study co-author, said spiders can be important bellwethers of environmental change.

“Spiders are very important to local ecosystems, both as a predator of insects and as a major food source to larger animals like birds,” she said. “Understanding how to predict and mitigate ecosystem imbalance caused by the disruption of prey behavior due to climate change is critical.”

The study was funded by grants from the National Science Foundation.

Many of the paper’s eight co-authors conducted their research as undergraduates in Uetz’s lab. This experience can have a profound effect on a student’s academic trajectory, Uetz said.

When he was an undergraduate, his first research project helped him overcome a fear of spiders.

“Most people who study spiders will say they had a lifelong fascination with them — but not me,” he said. “I was five or six playing cops and robbers and put my hand at the bottom of a gutter downspout and a spider ran up my arm and I totally freaked out.”

Uetz took invertebrate zoology and biology classes from his mentors, Albion College professors Dean Dillery and Alan Brady. His fear of spiders turned into fascination.

“You model yourself off your mentors. Dean Dillery encouraged me to do research. And when it was done, he took me to an Entomology Society meeting in Lansing, Mich., to give a presentation. It was a really meaningful experience, so I try to do the same with my students,” he said.

More scientific organizations are offering opportunities to undergraduates to present research, he said. Uetz took several undergraduates to the Arachnological Society conference last year at Cornell University.

“When I started undergraduate research in the lab, I had no interest in pursuing a research career,” Gilbert said. “But by the end, I decided to ask if I could stick around and pursue a graduate degree in Dr. Uetz's lab.”

Today, she has a doctorate from UC and works as a data scientist at NASA.

“I think the benefit of undergraduate research is that you get a new perspective into how scientific research is done and you gain skills that can be applied to other careers,” she said.

Featured image at top: UC biologists discovered that rain can interfere with spider communication. Photo/Joseph Fuqua II/UC

A portrait of George Uetz on UC's Uptown Campus.

UC Professor George Uetz has dedicated his career to studying the unique behavior of spiders and other invertebrates in his biology lab. Photo/Lisa Ventre/UC

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